The objectives of this project are to identify the mechanism of the control of flagellar movement displayed by animal sperm during orientation in a chemical gradient. The biological system used is the chemotactic turning of hydroid and urochordate sperm to secretions produced by eggs or egg-associated reproductive structures. The research is intended to shed light on the following problems: 1. How do the attracting compounds act on the sperm to: a. alter flagellar motility and/or orientation to produce a turn in a known direction; b. effect perception of the sperm so that it is able to determine the direction of the gradient. 2. What is the chemical basis of the specificity of the chemotactic behavior? 3. Does chemotactic turning of sperm occur in other animals, particularly mammals? The methods applied to this research include high-speed cinephotomicrography of sperm flagella during turning maneuvers to determine the detailed shape of the wave form actually employed by the sperm; computer simulation of the flagellar behavior to determine internal and external constraints on the flagellum during turning; effects of specific cations on the ability of the sperm to perceive the attractant; ultrastructural analysis, particularly by comparison of transmission and freeze-fracture images, of the role of the cell membrane in turning; effects of anti-sperm antibodies on sperm attraction; statistical analysis of the path directions and aggregative behavior patterns of the sperm in known gradient systems; and the methods of analytical and synthetic organic chemistry.